Overview

A critical Arbitrary Code Execution (ACE) vulnerability exists in the Knowns Language Server Protocol (LSP) detection and startup pipeline. The system blindly trusts the settings.lsp.languages.<lang>.binary field defined in the project-level .knowns/config.json file.

Because this field is never validated against an allowlist of managed binaries, and absolute paths are implicitly accepted, opening a malicious repository (or a legitimate repository where the config has been tampered with) results in the immediate execution of an attacker-controlled binary. The payload is executed twice per session: once during the initial runVersionCheck (health check), and again when the LSP server process is spawned via Server.Start(). When chained with the previously identified Config Overwrite vulnerabilities, this flaw yields a fully unauthenticated Remote Code Execution chain.

Affected paths

Root Cause

Missing Validation in Configuration Schema

In internal/models/config.go, the ProjectSettings.Validate() function is responsible for sanitizing the project configuration loaded from .knowns/config.json. However, it only validates task lifecycle durations:

func (s ProjectSettings) Validate() error {
    settings := s.EffectiveTaskLifecycle()
    if _, err := ParseTaskLifecycleDuration(settings.ArchiveAfter); err != nil { ... }
    // NO VALIDATION FOR s.LSP.Languages[lang].Binary
    return nil
}

The LSPLanguageSettings struct exposes a Binary string field. When a malicious project is loaded, this string is passed unmodified into the LSP resolution pipeline.

Blind Execution in LSP Detector

In internal/lsp/detect.go, the Detector.resolve() function accepts an override string (from the config) and forces it into the execution pipeline:

func (d *Detector) resolve(ctx context.Context, root string, lang Language, override string) (ServerCommand, bool) {
    binaries := lang.Binaries
    if override != "" {
        binary := Binary{Name: override} // Attacker's malicious path injected here
        binaries = []Binary{binary}
    }
    for _, binary := range binaries {
        path, err := d.LookPath(binary.Name) // Accepts absolute paths (e.g., /tmp/evil.sh)
        // ...
        err = d.RunCheck(checkCtx, path, binary.CheckArgs...) // EXECUTION #1
        // ...
    }
}

d.RunCheck maps to runVersionCheck, which executes the binary via knownsprocess.CommandContext(ctx, path, args...).Run().

Unrestricted Process Spawn

In internal/lsp/server.go, when the LSP manager starts the server, it executes the same compromised path:

func (s *Server) Start(ctx context.Context) error {
    // ...
    cmd := knownsprocess.Command(s.Command.Path, s.Command.Args...) // EXECUTION #2
    cmd.Dir = s.Root
    // ...
    if err := cmd.Start(); err != nil { ... }
}

Attack Vector

Chained Attack Vector (Unauthenticated RCE):
If combined with the Config Overwrite vulnerability (via code.replace path traversal), a remote attacker can overwrite .knowns/config.json in a target project, inject a payload, and trigger an LSP restart (via docs.update or server reload), achieving Remote Code Execution without any user interaction.

Analysis

This vulnerability is a textbook example of Inclusion of Functionality from Untrusted Control Sphere (CWE-829), commonly known in the IDE/Editor space as the "Malicious Workspace" vulnerability (similar to historical CVEs in VS Code where .vscode/settings.json could point to malicious interpreter paths).

The core failure is the lack of a strict allowlist for executable paths. By relying on exec.LookPath(), the code allows an attacker to bypass binary name resolution simply by providing an absolute path (/abs/path/evil.sh) or a path containing a slash (./evil.sh).

Furthermore, the execution happens automatically upon project load. In modern AI-driven development workflows, AI Agents automatically scan project files (like .go, .ts, .py) to provide context. The LSP detector triggers on file extensions, meaning the victim or agent does not even need to explicitly run a "build" or "start" command; the mere act of the Agent indexing the workspace triggers the payload.

Fix

Patch is available right now at New Release.

References

• GHSA-mc52-mwq4-vfx3
• https://nvd.nist.gov/vuln/detail/CVE-2026-86540
• knowns-dev/knowns@d398982
• https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/lsp/detect.go#L128-L157
• https://github.com/knowns-dev/knowns/blob/v0.29.1/internal/models/config.go#L205-L216
• https://github.com/knowns-dev/knowns/releases/tag/v0.30.0
• https://www.vulncheck.com/advisories/knowns-before-0.30.0-arbitrary-code-execution-via-lsp-binary